The stator end windings and phase rings of a typical hydrogen cooled generator are cooled by being enclosed in a casing at one end of the generator. Typically the generators cooling system comprises a fan circulating pressured hydrogen cooled by water. For efficient cooling the phase rings may be cooled in conjunction with the stator end windings but more typically, due to the cooling demand of the phase rings, they are independently cooled by means of ducting used to divert part of the cooling hydrogen inside the phase rings and return it back to the cooling medium heat exchanger. However ducting increases design complexity, due to the special requirements of hydrogen cooling and layout complexity, as a result of the number of phase rings present in multiphase generators.
Bushings are used to convey current from phase rings through the casing, while maintaining electrical insulation and ensuring the casing remains sealed, by radially extending without inclination through and outwards from the casing. The bushing ends outside of the casing are connected to insulated busbars and subsequently to a matrix converter. The radial positioning of the bushings minimises overall machine length however overall the design is not space efficient. Not only does it require significant radial space it also requires space to accommodate connecting cables. This problem is particularly acute for machines and generators with greater than three phases due to the number and complexity of the phase ring connections.